Fluid operated valves are used in oil and gas wells to permit controlled down hole injection into the well of materials such as corrosion and demulsifying inhibitors from the annulus between the tubing string and the casing into the tubing string. Such valves can be provided with a bellows which operates in conjunction with an optional valve spring for biasing the valve toward a closed position. Pressure of fluid is exerted on a piston opposite the bellows to open the valve. When the combined pressure of the fluid head in the casing annulus and pressure exerted by a chemical pump at the surface of the ground exceed the combined forces of the bellows and the optional valve spring, the valve is opened permitting flow from the annulus through the valve into the tubing string. Such valves are described in composite catalog of oil field equipment and services.
Heretofore difficulty has been encountered in installing chemical injector valves in deep hot wells. The bellows chamber is generally pressurized to an initial charging pressure at a facility remote from the well site and is charged at ambient temperature. These initial charging pressures in some wells are required to be very high for example in the range of 900 to 15,000 psig. During this charging operation, the bellows can be damaged or ruptured as a result of the excessive charging pressures.